This invention relates to a pneumatic radial tire which reduces a road noise having a vibration peak in a high frequency range of higher than 250 Hz.
As automobiles have been graded up in recent years, reduction of a road noise generated by the transmission of vibration of tires during driving into the car cabin has become a serious problem.
The road noise varies with a frequency, and includes a road noise having a vibration peak in a relatively low frequency range of about 100 to about 200 Hz (hereinafter referred to as the "low frequency range road noise") and a road noise having a vibration peak in a high frequency range of about 250 to about 400 Hz (hereinafter referred to as the "high frequency range road noise"). This former, that is, the low frequency range road noise, can be reduced relatively easily by increasing a rubber weight at a tread or reducing a spring constant of the tread so as to reduce an intrinsic vibration of a sidewall, and making different this intrinsic vibration from acoustic characteristics inside a car cabin.
As means for reducing the latter, that is, the high frequency range road noise, Japanese Patent Laid-Open No. 253406/1991 increases a rigidity by disposing locally a reinforcing member on an upper portion of sidewalls. However, the mere disposition of the reinforcing layer on the upper portion of sidewalls cannot reduce reliably and effectively the high frequency range road noise as will be obvious from the following description of the present invention.